The Environmental Protection Agency proposed major changes Thursday to an Obama-era initiative regulating coal ash waste, giving states and utilities more latitude in how they dispose of the toxic substance.

The proposal marks a major policy shift with ramifications for both the coal industry and communities across the country. It includes more than a dozen suggested changes for how coal ash — which has contaminated waterways in two high-profile spills during the past decade — is stored at more than 400 coal-fired power plants around the country. And in modeling the rule on 1991 standards for disposal of household trash in solid waste landfills, it would extend how long companies can maintain unlined coal ash ponds and let states alter how frequently they would test for groundwater contamination.

EPA Administrator Scott Pruitt said in a statement that the changes, which are estimated to save companies between $32 million and $100 million in annual compliance costs, underscore the administration’s commitment to federalism.

“Today’s coal ash proposal embodies EPA’s commitment to our state partners by providing them with the ability to incorporate flexibilities into their coal ash permit programs based on the needs of their states,” Pruitt said.

Federal regulators have long wrestled with how to address coal ash, the substance that remains when coal is burned in power plants to generate electricity. Containing a toxic mix of mercury, cadmium, arsenic and other heavy metals, coal ash can pollute waterways, poison wildlife and cause respiratory illness among people living near the massive pits in which plant operators store the waste.

After extensive negotiations with utilities, other affected industries and environmentalists, the Obama administration finalized regulations in 2015 that imposed new standards on coal-ash disposal sites, in part by increasing inspections and monitoring and requiring measures such as liners in new waste pits to prevent leaks that might threaten nearby drinking water supplies. The rules did not classify coal ash as a hazardous substance, which could have led to stricter requirements and made its recycling, to make concrete, gypsum wallboard and pavement, more difficult.

But last spring, shortly after the Trump administration took office, industry officials began lobbying the EPA to revisit the rules. They wrote that the existing regulation “is causing significant adverse impacts on coal-fired [power] generation in this country due to the excessive costs of compliance.”

Pruitt seemed sympathetic, saying in September that it was “appropriate and in the public interest” for the agency to rethink the regulations.

Quin Shea, the vice president for environment at the industry trade group Edison Electric Institute, praised Pruitt’s latest decision.

“The proposed rule will provide states and the industry with greater certainty as they work to close ash basins safely and responsibly and continue to manage other ash management facilities such as landfills,” Shea said in a statement.

The EPA said Thursday that itwill accept public comment on its proposal for 45 days after publication in the Federal Register, as well as hold a hearing on the potential changes. It then “plans to move quickly to take final action after the close of the comment period.”

Frank Holleman, a senior lawyer at the Southern Environmental Law Center, said in a statement that the changes the EPA has outlined would allow companies to circumvent the protections provided under the original rule.

“Coal ash is polluting rivers, lakes and wells across America, but President Trump’s EPA is trying to weaken the standards that are supposed to protect Americans from this toxic threat,” Holleman said. “These proposals will weaken rules that protect our groundwater from arsenic and mercury and continue to extend the use of unlined, leaking coal ash pits next to our waterways. America’s families and clean water deserve better.”

Lisa Evans, a senior attorney at Earthjustice, said in an interview Friday that the original rule had established “black-and-white requirements. Pruitt is turning it all gray.”

She noted that the proposal, which includes a lengthy preamble suggesting the agency might loosen restrictions much further when it finalizes the rule, leaves open the possibility of letting utilities determine when the groundwater should be tested. That would allow state regulators, rather than a technical expert, to make several determinations, she added, including whether a pit closure can be postponed due to a lack of storage capacity elsewhere and what sort of groundwater monitoring should take place once a pit is closed.

“This rule potentially turns over the reins to the polluter,” Evans said.

Environmental advocates said the significance of the changes was underscored on Friday, when utilities faced a deadline under the existing rule to report monitoring data for groundwater pollution at unlined coal ash lagoons. Without those requirements, Holleman said, residents in communities around the country would remain in the dark about potential risks to their drinking water.

“Toxic pollution that exceeds limits would require utilities to stop their coal ash pollution and restore our water resources to natural conditions,” he said. “But, giving a favor to industry lobbyists, the Trump administration … wants to weaken this provision and protect the polluters instead of the people and clean water.”

The short comment period, coupled with the fact that EPA has raised the prospect of additional changes, makes it harder for administration critics to raise objections that could be grounds to challenge any final agency decision in court, she added.

While there have been dozens of minor coal ash spills in recent years, two accidents wreaked havoc in the South. In February 2014, an underground pipe burst at a Duke Energy steam station in North Carolina, spilling tens of thousands of tons of coal ash into the Dan River. According to the EPA, the waste contained a long list of various metals, including arsenic, copper, lead and mercury.

The spill covered more than 70 miles of the river, home to two types of endangered species. The Dan is used by livestock and for crop irrigation and is a popular spot for fishing, kayaking and canoeing. In addition, the river is a source of drinking water for residents in North Carolina and Virginia.

State regulators eventually fined Duke more than $6 million, and legislators required the utility to close all of its existing coal ash storage ponds by 2029. The EPA also entered into a $3 million cleanup agreement with the company, which required Duke to remove coal ash deposits along the river.

In 2008, a dike failure at the Tennessee Valley Authority’s Kingston Fossil Plant released 5.4 million cubic yards of coal ash, sending much of it barreling into the Emory River and smothering several hundred acres of land.

A wave of sludge mowed down trees, destroyed power lines and damaged numerous homes, leaving several of them uninhabitable. The episode remains one of the largest coal ash spills in U.S. history, and TVA has spent more than $1 billion on cleanup efforts.

Brady DennisBrady Dennis is a national reporter for The Washington Post, focusing on the environment and public health issues. He previously spent years covering the nation’s economy. Dennis was a finalist for the 2009 Pulitzer Prize for a series of explanatory stories about the global financial crisis. Follow

Juliet EilperinJuliet Eilperin is The Washington Post's senior national affairs correspondent, covering how the new administration is transforming a range of U.S. policies and the federal government itself. She is the author of two books — one on sharks and another on Congress, not to be confused with each other — and has worked for The Post since 1998. Follow